TST: Fix Astropy minversion for Lorentz1D result change

The patch was backported and is now in Astropy 6.3.1,
which should be the minversion.

ginga/tests/test_iqcalc.py

@@ -10,7 +10,7 @@
 from ginga.util.iqcalc import have_scipy  # noqa
 from ginga.util.iqcalc_astropy import have_photutils  # noqa
 
-ASTROPY_LT_7_0 = not minversion("astropy", "7.0.dev")
+ASTROPY_LT_6_3_1 = not minversion("astropy", "6.3.1")
 
 
 @pytest.mark.parametrize(
@@ -287,7 +287,7 @@ def setup_class(self):
         self.fwhm_funcs = (self.iqcalc.calc_fwhm_gaussian,
                            self.iqcalc.calc_fwhm_moffat,
                            self.iqcalc.calc_fwhm_lorentz)
-        if ASTROPY_LT_7_0:
+        if ASTROPY_LT_6_3_1:
             lorentz_ans = (1.9570, 1.8113)
         else:
             # https://github.com/astropy/astropy/pull/16794